This invention relates to pnuematic systems for conveying solid particulate matter and particularly to a system for off loading solid particulate matter from an over-the-road dry bulk carrier.
Conventional over the road dry bulk carriers include a truck/tractor which pulls a trailer having a vessel thereon adapted to receive, store and discharge solid particulate matter, commonly known as dry bulk material such as flour, sugar, cement, etc. The conventional vessel has inlet apertures in the top thereof for receiving the dry bulk material from large storage hoppers, silos or the like. The bottom of the vessel has one or more tapering portions which terminate in a discharge aperture.
One common method of unloading the dry bulk material from the vessel is by use of a pnuematic conveying system. In a system such as this, the vessel is pressurized to a predetermined level, for example 12 to 15 PSI, by a blower. After the pressure within the vessel has reached the predetermined level, the air from the blower is diverted from pressurizing the vessel to pnuematic lines which flow past the outlet apertures of the vessel. When the outlet apertures are open, the combination of the pressure within the vessel and the venturi effect created by the air flowing past the outlet aperture causes the dry bulk material to be discharged from the vessel into the line carrying the air past the discharge apertures. This line is normally connected to the top of a using vessel, for example a storage hopper. The blower continues to force air past the outlet apertures until the vessel has been unloaded.
Various types of blowers have been used in off-loading systems of the type described above. One type of blower uses the exhaust from the tractor engine to drive a turbine. This is not only a relatively inefficient type of blower, it tends to have a detrimental effect on the engine, for example creating a back pressure which could burn the engine valves, and also tends to produce high air temperatures, for example on the order of 350.degree.. Although this high temperature air would have little effect on a material such as cement, it could have a significant detrimental effect on other materials such as flour or particulate plastic materials.
Another type of blower which has been used is mounted on the trailer and requires a pony motor to drive it. This combination is not only heavy, the pony motor sometimes proves difficult to start especially in colder weather.
Another type of blower is driven from a power take-off unit connected to the tractor engine. Blowers of this type are generally very noisy since high noise levels appear to be more tolerable in systems designed for outdoor operation.